Designer atomic layer etching

ABSTRACT

Methods for evaluating synergy of modification and removal operations for a wide variety of materials to determine process conditions for self-limiting etching by atomic layer etching are provided herein. Methods include determining the surface binding energy of the material, selecting a modification gas for the material where process conditions for modifying a surface of the material generate energy less than the modification energy and greater than the desorption energy, selecting a removal gas where process conditions for removing the modified surface generate energy greater than the desorption energy to remove the modified surface but less than the surface binding energy of the material to prevent sputtering, and calculating synergy to maximize the process window for atomic layer etching.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. Provisional Patent ApplicationNo. 62/436,286, filed Dec. 19, 2016, and titled “DESIGNER ATOMIC LAYERETCHING,” and U.S. Provisional Patent Application No. 62/532,916, filedJul. 14, 2017, and titled “DESIGNER ATOMIC LAYER ETCHING,” which areincorporated by reference herein in their entireties and for allpurposes.

BACKGROUND

Semiconductor fabrication processes include etching of variousmaterials. As feature sizes shrink, there is a growing need for atomicscale processing such as Atomic Layer Etch (ALE). However, performingALE in a self-limiting manner without sputtering for a variety ofmaterials is challenging.

SUMMARY

Methods and apparatuses for processing semiconductor substrates aredescribed herein. One aspect involves a method of etching a material ona substrate, the method including: identifying process conditions for anatomic layer etching process of the material using a modification gasand a removal gas; and performing the atomic layer etching process onthe material on the substrate by: exposing the substrate to themodification gas to modify a surface of the material, the modificationgas having a modification energy and a desorption energy with respect tothe material to be etched, and exposing the modified surface to theremoval gas and igniting a plasma to remove the modified surface,whereby the modification energy is less than the desorption energy, andthe desorption energy is less than a surface binding energy of thematerial.

In various embodiments, identifying the process conditions includesselecting a substrate temperature for performing the exposing thesubstrate to the modification gas, such that the energy provided by thesubstrate temperature is between the modification energy and thedesorption energy.

In various embodiments, identifying the process conditions includesselecting a bias power for applying a bias during the exposing themodified surface to the removal gas, such that the energy provided bythe bias is between the desorption energy and the surface bindingenergy.

In various embodiments, the modification gas is selected to adsorb tothe material without etching the material.

In various embodiments, the removal gas is selected to remove themodified surface without etching underlying unmodified material.

In some embodiments, the process conditions may be any one or more of:temperature, chamber pressure, plasma power, bias power, modificationgas flow, and exposure time.

The method may also include modifying the process conditions within aprocess window. The process window may be defined by a minimum andmaximum bias power delivered to a pedestal holding the substrate suchthat the minimum bias power is the minimum used to remove the modifiedsurface and the maximum bias power is the highest bias that can be usedwithout sputtering the material underlying the modified surface.

In various embodiments, the material is any one of silicon, carbon,tungsten, and tantalum. In some embodiments, the method also includescooling the substrate to a temperature less than about 0° C. prior toperforming the atomic layer etching process, whereby the processcondition identified is temperature, and whereby the material istantalum.

In various embodiments, the substrate is exposed to the modification gasat a substrate temperature less than about 0° C. In some embodiments,the temperature is between about −20° C. and about 0° C.

In some embodiments, the modification gas is a halogen-containing gas.In some embodiments, the removal gas is an inert gas.

In various embodiments, the atomic layer etching also includes purging achamber housing the substrate between the exposing the substrate to themodification gas and the exposing the substrate to the removal gas.

Another aspect involves a method of etching tantalum on a substrate, themethod including: providing the substrate including tantalum; coolingthe substrate to a temperature less than about 0° C.; and performingatomic layer etching of the tantalum by: exposing the substrate to amodification gas to modify a surface of the tantalum, and exposing themodified surface to a removal gas and igniting a plasma to remove themodified surface of the tantalum.

In various embodiments, the substrate is exposed to the modification gasat a substrate temperature less than about 0° C. In some embodiments,the temperature is between about −20° C. and about 0° C.

In various embodiments, the substrate includes tantalum nitride. In someembodiments, the method also includes purging a chamber housing thesubstrate between the exposing the substrate to the modification gas andthe exposing the substrate to the removal gas. Purging can be done usingany inert gas such as N₂, Ar, Ne, He, and their combinations.

In some embodiments, the modification gas is chlorine. In someembodiments, the modification gas is any one or more of bromine, iodine,sulfur hexafluoride, silicon tetrafluoride, and boron trichloride(BCl₃).

In various embodiments, the removal gas is argon. In some embodiments,neon or krypton may be used. In a removal operation, the substrate maybe exposed to an energy source (e.g. activating or ion bombardment gasor chemically reactive species that induces removal), such as argon orhelium, to etch the substrate by providing enough energy to desorb themodified tantalum surface but insufficient to sputter the tantalum suchthat energy is less than the surface binding energy. In someembodiments, removal may be isotropic.

In various embodiments, a bias is applied to at least one of theexposing the substrate to the modification gas and the exposing themodified surface to the removal gas. The bias power may be selecteddepending on the threshold sputter yield of the activated removal gaswith the deposited metal on the substrate.

Another aspect involves apparatus for processing a substrate, theapparatus including: a process chamber including a showerhead and asubstrate support for holding the substrate having a material, a plasmagenerator, and a controller having at least one processor and a memory,whereby the at least one processor and the memory are communicativelyconnected with one another, the at least one processor is at leastoperatively connected with flow-control hardware, and the memory storesmachine-readable instructions for: causing identification of processconditions for an atomic layer etching process of the material using amodification gas and a removal gas; and causing performance of theatomic layer etching process on the material on the substrate by:causing introduction of a modification gas to modify a surface of thematerial, the modification gas having a modification energy and adesorption energy with respect to the material to be etched, and causingintroduction of the removal gas and generation of a plasma to remove themodified surface, whereby the modification energy is less than thedesorption energy, and the desorption energy is less than a surfacebinding energy of the material.

In various embodiments, instructions for causing introduction of theprocess conditions includes instructions for causing selection of asubstrate temperature for performing the exposing the substrate to themodification gas, such that the energy provided by the substratetemperature is between the modification energy and the desorptionenergy.

In various embodiments, instructions for causing introduction of theprocess conditions includes instructions for causing selection of a biaspower for applying a bias during the exposing the modified surface tothe removal gas, such that the energy provided by the bias is betweenthe desorption energy and the surface binding energy.

In various embodiments, the modification gas is selected to adsorb tothe material without etching the material. In various embodiments, theremoval gas is selected to remove the modified surface without etchingunderlying unmodified material.

In some embodiments, instructions for causing introduction of theprocess conditions includes instructions for causing selection of theprocess conditions from any one or more of: temperature, chamberpressure, plasma power, bias power, modification gas flow, and exposuretime.

The apparatus may also include instructions for causing modification ofthe process conditions within a process window. The process window maybe defined by a minimum and maximum bias power delivered to a pedestalholding the substrate such that the minimum bias power is the minimumused to remove the modified surface and the maximum bias power is thehighest bias that can be used without sputtering the material underlyingthe modified surface.

In various embodiments, instructions for causing performance of theatomic layer etching also includes instructions for causing purging ofthe process chamber housing the substrate between instructions forcausing introduction of the modification gas and the causing of theintroduction of the removal gas.

Another aspect involves an apparatus for processing a substrate, theapparatus including: a process chamber including a showerhead and asubstrate support for holding the substrate, a plasma generator, and acontroller having at least one processor and a memory, whereby the atleast one processor and the memory are communicatively connected withone another, the at least one processor is at least operativelyconnected with flow-control hardware, and the memory storesmachine-readable instructions for: causing the temperature of thesubstrate support having the substrate including tantalum to be set to atemperature less than about 0° C.; and causing performance of atomiclayer etching of the tantalum by: causing introduction of a modificationgas to modify a surface of the tantalum, and causing the introduction ofa removal gas and generation of a plasma to remove the modifiedtantalum.

In various embodiments, the instructions for causing the temperature ofthe substrate support to be set to a temperature less than about 0° C.includes instructions for causing the temperature of the substratesupport to be set to a temperature between about −20° C. and about 0° C.

In various embodiments, instructions for causing performance of theatomic layer etching of the tantalum also includes instructions forcausing purging of the process chamber housing the substrate betweeninstructions for causing introduction of the modification gas and thecausing of the introduction of the removal gas. Purging can be doneusing any inert gas such as N₂, Ar, Ne, He, and their combinations.

In various embodiments, the memory further stores instructions forcausing a bias to be applied to the substrate support for holding thesubstrate during at least one of the introduction of the modificationgas and introduction of the removal gas. The bias power may be selecteddepending on the threshold sputter yield of the activated removal gaswith the deposited metal on the substrate.

These and other aspects are described further below with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows example schematic diagrams of substrates undergoing atomiclayer etching.

FIG. 1B shows the synergy of atomic layer etching based on the schematicdiagrams of substrates from FIG. 1A.

FIG. 2 is a process flow diagram depicting operations for a method inaccordance with disclosed embodiments.

FIG. 3 shows energy barriers for silicon, germanium, tungsten, carbon,and tantalum for E_(mod), E_(des), and E_(O).

FIG. 4 is a graph of surface binding energies of elements in theperiodic table of elements.

FIG. 5A shows a graph of sputter thresholds as a function of surfacebinding energy for various materials.

FIG. 5B shows a graph of synergy as a function of surface binding energyfor various materials.

FIG. 5C shows a graph of etch per cycle as a function of surface bindingenergy for various materials.

FIG. 6 is a process flow diagram depicting operations for a method inaccordance with disclosed embodiments.

FIG. 7 is a schematic diagram of an example process chamber forperforming disclosed embodiments.

FIG. 8 is a schematic diagram of an example process apparatus forperforming disclosed embodiments.

FIG. 9A is a graph of etch rate for tantalum shown as a function oftemperature as determined by experimental data.

FIG. 9B is a graph of etch per cycle and duration of exposures to argonfor tantalum using atomic layer etch in accordance with an experimentconducted.

FIG. 9C is a graph of etch per cycle and bias power applied to thepedestal during removal using argon for tantalum by atomic layer etch inaccordance with an experiment conducted.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the presented embodiments. Thedisclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Etching processes often involve exposing a material to be etched to acombination of etching gases to remove the material. However, suchremoval may not be self-limiting and in some cases may etch more thandesired, or result in an undesirable feature profile. As feature sizesshrink, there is a growing need for atomic scale processing such asAtomic Layer Etch (ALE). Atomic layer etch is a cyclic process ofnominally self-limiting steps that result in digital and small changesin film thicknesses. The process is characterized by smoothness andconformality, and also directionality in the case of some ALE.

ALE is a multi-step process used in advanced semiconductor manufacturing(e.g. technology node <10 nm) for the blanket removal orpattern-definition etching of ultra-thin layers of material with atomicscale in-depth resolution and control. ALE is a technique that removesthin layers of material using sequential self-limiting reactions.Generally, ALE may be performed using any suitable technique. Examplesof atomic layer etch techniques are described in U.S. Pat. No.8,883,028, issued on Nov. 11, 2014; and U.S. Pat. No. 8,808,561, issuedon Aug. 19, 2014, which are herein incorporated by reference forpurposes of describing example atomic layer etch and etching techniques.In various embodiments, ALE may be performed with plasma, or may beperformed thermally.

ALE may be performed in cycles. The concept of an “ALE cycle” isrelevant to the discussion of various embodiments herein. Generally anALE cycle is the minimum set of operations used to perform an etchprocess one time, such as etching a monolayer. The result of one cycleis that at least some of a film layer on a substrate surface is etched.Typically, an ALE cycle includes a modification operation to form areactive layer, followed by a removal operation to remove or etch onlythis modified layer. The cycle may include certain ancillary operationssuch as sweeping one of the reactants or byproducts. Generally, a cyclecontains one instance of a unique sequence of operations. As an example,an ALE cycle may include the following operations: (i) delivery of areactant gas, (ii) purging of the reactant gas from the chamber, (iii)delivery of a removal gas and an optional plasma, and (iv) purging ofthe chamber. In some embodiments, etching may be performednonconformally. FIG. 1A shows two example schematic illustrations of anALE cycle. Diagrams 171 a-171 e show a generic ALE cycle. In 171 a, thesubstrate is provided. In 171 b, the surface of the substrate ismodified. In 171 c, the next step is prepared. In 171 d, the modifiedlayer is being etched. In 171 e, the modified layer is removed.Similarly, diagrams 172 a-172 e show an example of an ALE cycle foretching a silicon film. In 172 a, a silicon substrate is provided, whichincludes many silicon atoms. In 172 b, reactant gas chlorine isintroduced to the substrate which modifies the surface of the substrate.The schematic in 172 b shows that some chlorine is adsorbed onto thesurface of the substrate as an example. Although chlorine is depicted inFIG. 1A, any chlorine-containing compound or suitable reactant may beused. In 172 c, the reactant gas chlorine is purged from the chamber. In172 d, a removal gas argon is introduced with a directional plasma asindicated by the Ar⁺ plasma species and arrows, and ion bombardment isperformed to remove the modified surface of the substrate. During thisoperation, a bias is applied to the substrate to attract ions toward it.In 172 e, the chamber is purged and the byproducts are removed.

A cycle may only partially etch about 0.1 nm to about 50 nm of material,or between about 0.1 nm and about 20 nm of material, or between about0.1 nm and about 2 nm of material, or between about 0.1 nm and about 5nm of material, or between about 0.2 nm and about 50 nm of material, orbetween about 0.2 nm and about 5 nm of material. The amount of materialetched in a cycle may depend on the purpose of etching in aself-limiting manner. In some embodiments, a cycle of ALE may removeless than a monolayer of material.

ALE process conditions, such as chamber pressure, substrate temperature,plasma power, frequency, and type, and bias power, depend on thematerial to be etched, the composition of the gases used to modify thematerial to be etched, the material underlying the material to beetched, and the composition of gases used to remove the modifiedmaterial. However, the combination of these factors make performing ALEfor etching a variety of materials challenging.

Given the increasing number of new materials being introduced intointegrated circuit processing and the large number of combinations ofprocess parameters (gas pressure, wafer temperature, plasma power, ionenergy, etc.), achieving an ALE process that does not sputter but alsoetches in a layer-by-layer self-limiting way for a given material ischallenging. A universally applicable tool to perform ALE processdevelopment is needed. In addition, having the ability to predict ALEperformance or even applicability would focus research and developmenton materials that are the most promising candidates for ALE.

Provided herein is a method of performing “designer” ALE based on an“ALE synergy” metric for the material to be etched. Disclosedembodiments allow one to design an ALE process using the ALE synergymetric to achieve self-limiting removal of the material while reducingsputtering of the material to be etched, or removal or sputtering ofmaterial underlying the material to be etched. Alternately, for anexisting process tool and set of accessible process parameters,disclosed embodiments allow one to predict whether a given material canbe removed using ALE and, if so, the anticipated quality of the etching.In addition, disclosed embodiments can be used to maximize desired etchselectivity between materials, by designing one material to be etchedwhile another does not under the same conditions.

Disclosed embodiments are applicable to a wide class of materialsincluding semiconductors (e.g., silicon, germanium, silicon germanium(SiGe), gallium nitride (GaN); metals (e.g., tungsten, cobalt, copper,tantalum); dielectrics (e.g., silicon oxide (SiO₂), silicon nitride(SiN)); and ashable hard masks such as carbon. Disclosed embodiments arealso suitable for etching compounds such as nitrides and oxides. It canbe utilized to develop new or improved unit or integrated processes aswell as standalone or clustered hardware. The methodology can beimplemented with appropriate computer software for offline use orembedded in a process tool for recipe development, processqualification, or process control.

The methodology is universally applicable but can be customized for agiven material-process tool combination, lending itself toimplementation as a computer algorithm. Being based on atomistic energyconsiderations, the approach is inherently scalable and can be appliedto both present and future device technology nodes. Its ability topredict how well an ALE process is working or would work relative to theideal is an additional benefit of the approach.

Disclosed embodiments are suitable for performing ALE for a broad classof materials of interest in integrated circuit technology (e.g.semiconductors such as silicon, germanium, gallium nitride; metals suchas tantalum, tungsten, cobalt; dielectrics such as silicon oxide, andashable hardmask materials such as amorphous or diamond-like carbon). Inthe following discussion, non-limiting examples are provided for ALE ofsilicon (e.g. done by alternating Cl₂-plasma and Ar⁺ bombardment) andALE of tantalum.

ALE involves splitting the etch process into two (or more) separatesteps: modification (operation A) and removal (operation B). Forexample, the modification operation step modifies the surface layer sothat it can be removed easily during the removal operation. A thin layerof material is removed per cycle, where a cycle includes modificationand removal, and the cycle can be repeated until the desired depth isreached. Synergy means that favorable etching occurs due to interactionof operations A and B. In ALE, operations A and B are separated ineither space or time.

Favorable atomic layer etching occurs due to the interaction ofoperations A and B, and the following “ALE synergy” metric is used toquantify the strength and impact of the synergistic interaction. ALEsynergy is calculated by:

$\begin{matrix}{{{ALE}\mspace{14mu}{Synergy}\mspace{14mu}\%} = {\frac{{EPC} - \left( {A + B} \right)}{EPC} \times 100\%}} & \left( {{eqn}.\mspace{14mu} 1} \right)\end{matrix}$where EPC (“etch per cycle”) is the thickness of substrate materialremoved in one ALE cycle, typically averaged over many cycles, and A andB are contributions to the EPC from the stand-alone modification andremoval operations, respectfully, measured as reference points byperforming these operations independently.

Synergy is a test that captures many aspects of ALE behavior, and iswell-suited to compare different ALE conditions or systems. It is anunderlying mechanism for why etching in operation B stops afterreactants from operation A are consumed. It is therefore responsible forthe self-limiting behavior in ALE benefits such as aspect ratioindependence, uniformity, smoothness, and selectivity.

FIG. 1B is schematic illustration of ALE synergy illustrated forsilicon. By way of example, consider ALE of silicon carried out using achlorination operation A and argon ion bombardment operation B. If theoverall ALE process removes 1 nm/cycle, but only 0.1 nm/cycle from Aalone and 0.1 nm/cycle from B alone, then synergy is 80%. A high-synergyprocess might have synergy above about 90% as compared to below about60% for a low-synergy process.

Disclosed embodiments are structured to achieve an ALE process with highsynergy—the ideal being an ALE process with synergy being 100%. Thisideal may not be possible to achieve in all cases given practicalconsiderations such as the accessible range of process conditions, waferthroughput requirements, etc. However, tolerance for synergy less thanthe ideal of 100% will depend on the application and the technologynode, and presumably each successive technology generation will demandhigher levels of ideality.

Disclosed embodiments for designing an ALE process with high synergy isbased on achieving a hierarchical relationship between five definingenergies that characterize an overall ALE process and the energybarriers that are overcome to achieve etch with synergy close to 100%.

This relationship is as follows:E_(mod)<ε_(A)<E_(des)<ε_(B)<E_(O)  (eqn. 2)

The three energies written with upper case E's (E_(O), E_(mod), andE_(des)) are determined by properties of the material to be etched andthe reactant.

E_(O) is the surface binding energy of the unmodified material and isthe cohesive force that keeps atoms from being removed from the surface.Values are commonly estimated from heats of sublimation and aretypically in the range of 2-10 eV per atom.

E_(mod) is the adsorption barrier to modify the surface and arises fromthe need to dissociate reactants or reorganize surface atoms. Thisbarrier may be negligible when plasma is used to dissociate thereactants into radicals, such as during plasma chlorination of silicon.

The desorption barrier E_(des) is the energy used to remove a by-productfrom the modified surface. For example, in ALE of silicon, theby-product may be SiCl₂ (g) with about 2.9 eV desorption energy. Thisbarrier is related to volatility and thermal desorption temperatures.

Experimental values for the E's are found in chemical-physical handbooksand in published scientific papers or can be obtained from ab initiocalculations. By way of example, for silicon ALE with Ar⁺ ions/Cl₂,E_(mod)=0.3 eV<E_(des)˜2.9 eV<E_(O)=4.7 eV.

ε_(A) and ε_(B) are energies in the surroundings in operations A and B,respectively. In terms of rates, a given reaction will proceed if theenergy delivered is high enough as compared to the energy barrier. Thisenergy could be provided by a flux of suitably energetic ions,electrons, etc. (allowing the possibility of a directional energysource) or thermally with an Arrhenius-type relation for the temperaturedependence (viz, rate is or characterized by e^(−E/kT)).

ε_(A) and ε_(B) depend on equipment and process conditions and, withinthe accessible range of hardware and process parameters, are chosen toprovide a high-synergy ALE etch for a given material system.

With regard to temperature, increasing the average temperature by asmall amount could dramatically increase the delivered energy. Forexample, a gas satisfying a Maxwell-Boltzmann distribution has averageenergy <E>=3/2 kT. Raising temperature from, for example, roomtemperature of 25° C. (300K) to 325° C. (600K) will double <E>. However,the increase in high energy atoms in the exponential tail of thedistribution will increase far more than two times—in this case, thepopulation of atoms having E>1 eV increases by a factor of almost abillion.

The energy dependence of the removal rate for ions depends on the squareroot of ion energy relative to the threshold energy, with aproportionality constant that is inversely proportional to the surfacebinding energy E₀. With most of the incident ion's kinetic energydissipated as heat in atom-atom collisions, ion energy of about 20 timesthe barrier energy is used to provide sufficient energy source for ALE.For example, a 2.5 eV barrier may be overcome using incident ion energyof greater than about 50 eV since about 95% of the incident ions willnot be available to drive the ALE process after thermalizing with thewafer lattice.

The order of the inequalities in eqn. (2) indicates that the highestsynergy occurs when adsorption takes place without desorption inoperation A, and when desorption takes place without removing theunmodified material in operation B. This relation represents the energy“window” for the ALE process. Thus, E_(O) and E_(mod) set the upper andlower bounds of the inequality, so the larger their energy difference,the more latitude one has to achieve sufficient synergy.

The inter-related nature of the E's and epsilons shown in eqn. (2)underscores that fact that success of an ALE process will depend notonly on properties of the material-reactant combination (E's), but alsoon one's choice of reactor conditions (ε's) and energies to meet thecriteria for high synergy. Furthermore, throughput is also a factor, asovercoming the barrier depends on constraints in the operationtimes—analogous to the situation in which a chemical reaction may bethermodynamically favored (i.e. Gibbs free energy change is large andnegative) but where the kinetics are such that the reaction time isimpractically long.

Disclosed embodiments can also be used to design for etch selectivitybetween materials, by designing one material to etch while another doesnot under the same conditions. This is a potential benefit of themethodology, given the difficulty of achieving high etch selectivity(such as between a substrate and a masking layer, between a material tobe etched and an underlying etch stop layer, etc.)

A similar formalism to eqns. (1) and (2), and a similar methodologybased on first-principles energetic considerations can be developed forAtomic Layer Deposition (ALD), given that ALD and ALE are similar beingsequential, self-limiting, atomistic processes. In some embodiments, ALDand ALE may be combined in a series of operations used to fabricatesemiconductor devices. For example, further description regardingintegration of ALD and ALE are described in U.S. Pat. No. 9,576,811issued Feb. 21, 2017 entitled “INTEGRATING ATOMIC SCALE PROCESSES: ALD(ATOMIC LAYER DEPOSITION) AND ALE (ATOMIC LAYER ETCH)” which is hereinincorporated by reference in its entirety.

FIG. 2 provides a process flow diagram depicting operations forselecting the material to be etched, the reactants used to etch usingALE, and the process conditions to effectively etch using ALE withoutsputtering either the material to be etched or any underlying materialand without etching the material too quickly in a non-self-limitingmanner.

In operation 299, process conditions for atomic layer etching areidentified. Example process conditions include temperature, chamberpressure, plasma power, bias power, modification gas flow, and exposuretime. These process conditions may be process conditions used duringmodification, or during removal, or both. Example process conditionsinclude substrate temperature for performing the exposing the substrateto the modification gas, and bias power for applying a bias duringexposing of the modified surface to a removal gas, performed inoperation 211 as described below.

In operation 201, E_(O) is determined. E_(O) sets the upper energyboundary of the energy inequality given in Eqn. 2. E_(O) is determinedby the choice of material, so in effect choosing E_(O) is equivalent tochoosing the material to etch. If the choice of material is to bedetermined, one may select a material having an energy E_(O) as large aspossible since this would give the largest process window in which toachieve high synergy.

In operation 203, a reactant or modification gas for etching thematerial selected in operation 201 is chosen. This choice will dictatethe values of E_(mod) and E_(des) depending on the interaction of themodification gas with the film to be etched. The value for E_(mod)should be small enough to give flexibility for the choices of ε_(A) andε_(B) but large enough so that reactant will react but does not desorb(E_(des)>E_(mod)). These values can be estimated from ab initiocalculations or experimental tests with Arrhenius equation (for E_(mod))and from volatility measurements, ab initio calculations, or thermaldesorption temperatures (for E_(des)).

In operation 205, an energy delivery modality is selected such that themodality determines values for ε_(A) and ε_(B) wherebyE_(mod)<ε_(A)<E_(des)<ε_(B)<E_(O). These ε_(A) and ε_(B) valuesrepresent the useful energy delivered to the surface (e.g. energeticflux of ions, photons or electrons, chemical energy, etc.) or availablefrom the surroundings (e.g. substrate or plasma temperature). In variousembodiments, ε_(A) represents the energy applied during the modificationoperation (operation A), which is sufficient to modify the substrate(E_(mod)<ε_(A)), but low enough to prevent the modification gas fromreacting with the surface (ε_(A)<E_(des)). In various embodiments, ε_(B)represents the energy applied during the removal operation (operationB), which is sufficient to remove the modified surface (E_(des)<ε_(B)),and low enough to prevent sputtering of the material to be etched(ε_(B)<E_(O)). For any given material, depending on the modificationgas, E_(mod) and E_(des) may vary.

In the case of ALE of silicon using Cl₂ as a modification gas and Ar⁺ asa removal gas, EA can be determined by the temperature of the Cl₂(thermal) or the Cl₂ plasma, while ε_(B) can be determined by the usefulenergy delivered by the Ar ions. For example, if plasma is used, thiscan affect reaction pathway (and thus E_(mod) and E_(des)) and one mayselect a different modification gas. In various embodiments, the energyfor operation A, or ε_(A), is modulated by varying the temperature ofthe substrate during the modification operation, while the energy foroperation B, or ε_(B), is modulated by varying the plasma conditionsduring the removal operation (such as plasma power or bias power). Thus,to achieve ALE in a self-limiting manner, if the range between E_(mod)and E_(des) is small, the temperature range for performing themodification operation without causing desorption is small, and if therange between E_(mod) and E_(des) is large, the temperature range forperforming the modification operation without causing desorption islarge. If the range between E_(des) and E_(O) is small, the range ofprocess conditions for performing the removal operation withoutsputtering is small, while if the range between E_(des) and E_(O) islarge, the range of process conditions for performing the removaloperation without sputtering is large.

In operation 207 a, the synergy of the resulting ALE process ismeasured, and in operation 207 b, the ALE process conditions aremodified to increase the synergy further while still meeting Eqn 2 amongthe five energies. One could utilize a range of values and measure theindividual and synergistic etch rates to calculate the synergy. Forexample, if Ar⁺ ion bombardment is used, one could bias the wafer andrun through a range of ion energies (e.g. 10-100 eV). This can be usedto determine the bias window in which synergy is the highest.

In some embodiments, operation 201 may be repeated if the determinedsynergy is not a desired value. In some embodiments, operations 203 and205 may be performed repeatedly to evaluate the energy delivery modalityto select a modification gas having desirable synergy properties.

In operation 209, the substrate is exposed to the modification gasselected in operation 203 to modify the surface of the substrate basedon the process conditions selected.

In operation 211, the modified surface is removed from the substrate,using process conditions such as bias power modified in operation 207 bto maximize synergy. In some embodiments, operations 209 and 211 arerepeated.

Table 1 shows example synergies for ALE of various materials usingvarious modification gases for the modification operation and argonplasma for the removal.

TABLE 1 ALE Material ALE Modification Removal Measurements SiliconChlorine plasma 50 eV Ar+ Synergy = 90% EPC = 0.70 nm/cycle α = 0.03nm/cycle β = 0.04 nm/cycle Germanium Chlorine plasma 25 eV Ar+ Synergy =66% EPC = 0.80 nm/cycle α = 0.20 nm/cycle β = 0.07 nm/cycle AmorphousOxygen plasma 50 eV Ar+ Synergy = 97% carbon EPC = 0.31 nm/cycle α = 0nm/cycle β = 0.01 nm/cycle Tungsten Chlorine plasma 60 eV Ar+ Synergy =95% EPC = 0.21 nm/cycle α = 0 nm/cycle β = 0.01 nm/cycle Gallium nitrideChlorine plasma 70 eV Ar+ Synergy = 91% EPC = 0.33 nm/cycle α = 0nm/cycle β = 0.03 nm/cycle Silicon dioxide Chlorine plasma 70 eV Ar+Synergy = 80% EPC = 0.50 nm/cycle α = 0 nm/cycle β = 0.10 nm/cycle

Tantalum is used as a demonstrated example of determining how tomodulate process conditions for tantalum ALE using the operations ofFIG. 2. In operation 201, the value for E_(O) is determined bycalculating the surface binding energy of tantalum. Literature valuesare taken to evaluate the surface binding energy of tantalum.

In operation 203, a reactant is chosen based on E_(mod) and E_(d). Forexample, the adsorption barrier (E_(mod)) are taken to be ˜0 if plasmais used during modification. E_(des) is determined by estimating thethermal desorption temperatures which are found in literature for somereactant material systems. The energy delivery modality is determined inoperation 205 for ε_(A) and ε_(B). The synergy is then calculated inoperation 207 a, and the process conditions modified if needed inoperation 207 b. It will be understood that in various embodiments, anyone or more inert carrier gases (such as N₂, Ar, Ne, He, or combinationsthereof) may be flowed during any of the modification or the removaloperations. Additionally, for an ALE cycle, the chamber may be purgedafter modification, or after removal, or both in some embodiments. Insome embodiments, an ALE cycle includes modification, purge, removal,and purge. Purging may involve a sweep gas, which may be a carrier gasused in other operations or a different gas. In some embodiments,purging may involve evacuating the chamber.

FIG. 3 shows an example of how tantalum ALE works based on the relativeadsorption, desorption, and surface binding energies when chlorine isused as the modification gas and argon is used as the removal gasrelative to the ALE of other elemental materials. The surface bindingenergies E_(O) (black triangles) are determined by literature values, asin FIG. 4 which is further described below. The absorption barrierE_(mod) (striped shaded triangles) are taken to be ˜0 since plasma isused. The desorption energy E_(des) is inferred from the desorptiontemperature.

For all examples provided in FIG. 3, the E_(mod) is taken as about 0 eV.For silicon, the desorption temperature is 650° C. for SiCl₂, and theE_(des) is inferred from this temperature to be about 2.3 eV for etchingusing chlorine (to form by-product SiCl₂ when a silicon surface ismodified by chlorine). The surface binding energy of silicon is 4.7 eV.

For germanium, the desorption temperature is at 350° C. for GeCl₂, andE_(des) is inferred from this temperature to be between 1 and 2 eV (toform by product GeCl₂ when a germanium surface is modified by chlorine).The surface binding energy of germanium is 3.8 eV.

For tungsten, the E_(des) inferred from desorption temperature of about800° C. using chlorine as the modification gas is about 3 eV (to form abyproduct WCl₅ when a tungsten surface is modified by chlorine). Thesurface binding energy for tungsten is 8.8 eV.

For carbon, the E_(des) inferred from desorption temperature of about850° C. using oxygen as the modification gas is about 3 eV (to form abyproduct CO when a carbon surface is modified by oxygen). The surfacebinding energy for graphitic carbon is 7.4 eV.

For tantalum, the E_(des) inferred from desorption temperature of about23° C. using chlorine as the modification gas is about 1.5 eV (to form abyproduct TaCl₅ when a tantalum surface is modified by chlorine). Thesurface binding energy for tantalum is 8.1 eV.

The relative value for the desorption barrier (white triangles) isestimated based on thermal desorption temperatures, which are found inliterature for these reactant-material systems. The temperaturesindicated in FIG. 3 are the thermal desorption temperatures. The energybarriers for tantalum ALE suggest using low temperature duringmodification to suppress the chlorine reaction with tantalum, and alarge window during the removal operation with respect to ion energy.This is because the window between E_(mod) and E_(des) is very small,and given that the desorption energy at desorption temperature 250° C.is very small, the processing temperature for ALE of tantalum should below to ensure that the energy used during the modification operation(operation A) is within this small window to prevent chlorine fromreacting with tantalum in a non-self-limiting manner. However, given thelarge energy gap between E_(des) and E_(O), a wide range of ion energycan be used during the removal operation (operation B) without risk ofsputtering the tantalum surface given the high surface binding energy oftantalum.

FIG. 4 shows surface binding energy for elemental materials, asdetermined by heats of sublimation. According to this plot, carbon andthe refractory metals (W, Ta, Re, Nb, Mo, etc.) are good candidates forALE. Out of the other materials with surface binding energy greater thanabout 6 eV, tantalum is particularly useful as this material is used aspart of the barrier/liner in metallization in BEOL processing. Based onsurface binding energy, ALE of tantalum should work well.

FIGS. 5A-5C shows summary of material trends in ALE. As discussed, thetrends suggest that other materials with high surface binding energy aregood candidates for ALE. In FIG. 5A, the upper edge of window or thesputter threshold (as in the energy upon which the material would besputtered, rather than modified) is plotted against the surface bindingenergy E_(O). As shown, as the surface binding energy increases, theupper edge of the window increases. A higher upper edge of window allowsfor a broader range of energies that may be used to modify the materialwithout sputtering it.

FIG. 5B shows synergy as calculated by Eqn. 1 as a function of surfacebinding energy E_(O). As shown, as surface binding energy increases,synergy increases. These show that high surface binding energy materialsare more likely to have a high synergy effect, and thus are goodcandidates for ALE.

FIG. 5C shows the etch per cycle (EPC) in nm/cycle as a function ofsurface binding energy E_(O). As shown, as surface binding energyincreases, the etch per cycle decreases. That is, less material isetched per cycle. This suggests that high surface binding energymaterials are able to be more closely controlled for layer-by-layerself-limiting etching by ALE, whereas low surface binding energymaterials are more likely to etch faster by ALE.

For the example of tantalum, in various embodiments, tantalum may beetched using ALE in accordance with certain disclosed embodiments. Forexample, upon identifying E_(O), E_(des), and E_(mod) for using chlorine(as an example modification gas) for etching tantalum, a substratehaving tantalum may be etched using the following example method.

FIG. 6 shows an example process flow diagram of operations performed foratomic layer etching of tantalum in accordance with certain disclosedembodiments. As described above, after determining synergy for tantalum,atomic layer etching of tantalum can be achieved by toggling processconditions.

In operation 601, a substrate having tantalum is provided to a processchamber. The substrate may be a silicon wafer, e.g., a 200-mm wafer, a300-mm wafer, or a 450-mm wafer, including wafers having one or morelayers of material such as dielectric, conducting, or semi-conductingmaterial deposited thereon. A patterned substrate may have “features”such as vias or contact holes, which may be characterized by one or moreof narrow and/or re-entrant openings, constrictions within the features,and high aspect ratios. The features may be formed in one or more of theabove described layers. One example of a feature is a hole or via in asemiconductor substrate or a layer on the substrate. Another example isa trench in a substrate or layer. In various embodiments, the featuremay have an under-layer, such as a barrier layer or adhesion layer.Non-limiting examples of under-layers include dielectric layers andconducting layers, e.g., silicon oxides, silicon nitrides, siliconcarbides, metal oxides, metal nitrides, metal carbides, and metallayers. In various embodiments, the substrate includes tantalum ortantalum derivatives. In some embodiments, the substrate includestantalum nitride, or two or more layers of tantalum and/or tantalumnitride.

In operation 603, the substrate is exposed to a modification gas tomodify a surface of the tantalum at a low substrate temperature. Duringthis operation, or prior to introducing the gas but after providing thesubstrate to the process chamber, the substrate is cooled to a lowtemperature, a low temperature being a temperature at, about, or lessthan about 0° C., such as between −30° C. and about 0° C.

The modification gas modifies a surface of the tantalum such that theenergy applied during modification, such as low temperature, achieves anenergy between the modification energy (energy sufficient to modify thesurface) and the desorption energy. The temperature remains low toprevent the modification gas from reacting with the tantalum, as suchreaction would prevent the self-limiting behavior of atomic layeretching from being performed. For example, at a temperature of about 60°C., etching of the tantalum would occur when exposed to chlorine gas,therefore not resulting in an ALE process.

In various embodiments, the modification gas flow may be modulated tovary the amount of modification gas introduced to the substrate. Thesubstrate may be exposed to the modification gas for any suitableexposure time. In some embodiments, the substrate is exposed for anexposure time sufficient to adsorb the modification gas onto the surfaceof the tantalum. In some embodiments, the exposure time is at leastabout 1 second, or about 1 second, or about 2 seconds.

In some embodiments, during operation 603, a plasma is also ignited toform the modified surface of the tantalum. Plasma increases adsorptiontime by enabling faster adsorption kinetics. For example, plasma lowersenergy barrier E_(des) by converting the modification gas to radicals.In some embodiments, a chlorine-based plasma may be generated duringthis operation. The species generated from a chlorine-based plasma canbe generated in situ by forming a plasma in the process chamber housingthe substrate or they can be generated remotely in a process chamberthat does not house the substrate such as a remote plasma generator, andcan be supplied into the process chamber housing the substrate. Invarious embodiments, the plasma may be an inductively coupled plasma ora capacitively coupled plasma or a microwave plasma. Power for aninductively coupled plasma may be set at between about 50 W and about2000 W, such as about 900 W. Power may be set at a low enough level soas not to cause direct plasma etching of the substrate.

In a modification operation, a substrate may be modified using ahalogen-containing chemistry. For example, a substrate may bechlorinated by introducing chlorine into the chamber. Chlorine is usedas an example modification chemistry in disclosed embodiments, but itwill be understood that in some embodiments, a different modificationchemistry is introduced into the chamber. Examples include bromine,iodine, sulfur hexafluoride, silicon tetrafluoride, and borontrichloride (BCl₃).

In operation 605, the chamber is optionally purged. In a purgeoperation, non-surface-bound active chlorine species may be removed fromthe process chamber. This can be done by purging and/or evacuating theprocess chamber to remove non-adsorbed modification chemistry, withoutremoving the adsorbed layer. The species generated in a chlorine-basedplasma can be removed by stopping the plasma and allowing the remainingspecies to decay, optionally combined with purging and/or evacuation ofthe chamber. Purging can be done using any inert gas such as N₂, Ar, Ne,He, and their combinations.

In operation 607, the substrate is exposed to a removal gas and a plasmais ignited to remove the modified surface. In various embodiments, theremoval gas is argon. In some embodiments, neon or krypton may be used.In a removal operation, the substrate may be exposed to an energy source(e.g. activating or ion bombardment gas or chemically reactive speciesthat induces removal), such as argon or helium, to etch the substrate byproviding enough energy to desorb the modified tantalum surface butinsufficient to sputter the tantalum such that energy is less than thesurface binding energy. In some embodiments, removal may be isotropic.In some embodiments, the modified surface in operation 607 can beremoved by raising substrate temperature, but such removal is isotropic.For example, in some embodiments, removal using heat may be used fordesorption, but such removal may be isotropic.

The estimated rate of desorption is lower at higher temperatures thanlower temperatures, and thus in various embodiments, plasma is ignitedto increase the rate of desorption. Ions generated from the plasma allowfor removal at low temperatures using anisotropic etching. Using ionsallows an alternative technique to etch to perform etching directionallyand to perform an etching process that is not dependent on Arrheniusrate law. In some embodiments, a bias is applied during at least one ofoperation 607 and 603 to aid removal by atomic layer etching. It will beunderstood that substantial energy loss such as about 90% of energyoccurs due to collisions, and thus anisotropic etching by applying abias helps overcome energy losses to effectively remove a modifiedtantalum layer.

During removal, a bias may be optionally applied to facilitatedirectional ion bombardment. The bias power is selected to preventsputtering but allow the removal gas to enter the feature and etch thetungsten at or near the opening of the feature to thereby open it. Thebias power may be selected depending on the threshold sputter yield ofthe activated removal gas with the deposited metal on the substrate.Sputtering as used herein may refer to physical removal of at least someof a surface of a substrate. Ion bombardment may refer to physicalbombardment of a species onto a surface of a substrate.

In operation 609, the chamber is optionally purged to remove reactedby-products from the chamber. The chamber may be purged using any of thegases or techniques as described above with respect to operation 605.

As shown, in some embodiments, operations 603-609 may be optionallyrepeated as necessary to etch the desired amount of tantalum from thesubstrate.

Apparatus

Inductively coupled plasma (ICP) reactors which, in certain embodiments,may be suitable for atomic layer etching (ALE) operations are nowdescribed. Such ICP reactors have also described in U.S. PatentApplication Publication No. 2014/0170853, filed Dec. 10, 2013, andtitled “IMAGE REVERSAL WITH AHM GAP FILL FOR MULTIPLE PATTERNING,”hereby incorporated by reference in its entirety and for all purposes.Although ICP reactors are described herein, in some embodiments, itshould be understood that capacitively coupled plasma reactors may alsobe used.

FIG. 7 schematically shows a cross-sectional view of an inductivelycoupled plasma etching apparatus 700 appropriate for implementingcertain embodiments herein, an example of which is a Kiyo™ reactor,produced by Lam Research Corp. of Fremont, Calif. The inductivelycoupled plasma apparatus 700 includes an overall process chamber 701structurally defined by chamber walls 701 and a window 711. The chamberwalls 701 may be fabricated from stainless steel or aluminum. The window711 may be fabricated from quartz or other dielectric material. Anoptional internal plasma grid 750 divides the overall processing chamber701 into an upper sub-chamber 702 and a lower sub-chamber 703. In mostembodiments, plasma grid 750 may be removed, thereby utilizing a chamberspace made of sub-chambers 702 and 703. A chuck 717 is positioned withinthe lower sub-chamber 703 near the bottom inner surface. The chuck 717is configured to receive and hold a semiconductor wafer 719 upon whichthe etching and deposition processes are performed. The chuck 717 can bean electrostatic chuck for supporting the wafer 719 when present. Insome embodiments, an edge ring (not shown) surrounds chuck 717, and hasan upper surface that is approximately planar with a top surface of awafer 719, when present over chuck 717. The chuck 717 also includeselectrostatic electrodes for chucking and dechucking the wafer. A filterand DC clamp power supply (not shown) may be provided for this purpose.Other control systems for lifting the wafer 719 off the chuck 717 canalso be provided. The chuck 717 can be electrically charged using an RFpower supply 723. The RF power supply 723 is connected to matchingcircuitry 721 through a connection 727. The matching circuitry 721 isconnected to the chuck 717 through a connection 725. In this manner, theRF power supply 723 is connected to the chuck 717.

Elements for plasma generation include a coil 733 is positioned abovewindow 711. In some embodiments, a coil is not used in disclosedembodiments. The coil 733 is fabricated from an electrically conductivematerial and includes at least one complete turn. The example of a coil733 shown in FIG. 7 includes three turns. The cross-sections of coil 733are shown with symbols, and coils having an “X” extend rotationally intothe page, while coils having a “●” extend rotationally out of the page.Elements for plasma generation also include an RF power supply 741configured to supply RF power to the coil 733. In general, the RF powersupply 741 is connected to matching circuitry 739 through a connection745. The matching circuitry 739 is connected to the coil 733 through aconnection 743. In this manner, the RF power supply 741 is connected tothe coil 733. An optional Faraday shield 749 is positioned between thecoil 733 and the window 711. The Faraday shield 749 is maintained in aspaced apart relationship relative to the coil 733. The Faraday shield749 is disposed immediately above the window 711. The coil 733, theFaraday shield 749, and the window 711 are each configured to besubstantially parallel to one another. The Faraday shield may preventmetal or other species from depositing on the dielectric window of theplasma chamber 701.

Process gases (e.g. chlorine, argon, oxygen, etc.) may be flowed intothe processing chamber 701 through one or more main gas flow inlets 760positioned in the upper chamber 702 and/or through one or more side gasflow inlets 770. Likewise, though not explicitly shown, similar gas flowinlets may be used to supply process gases to a capacitively coupledplasma processing chamber. A vacuum pump, e.g., a one or two stagemechanical dry pump and/or turbomolecular pump 740, may be used to drawprocess gases out of the process chamber 701 and to maintain a pressurewithin the process chamber 701. For example, the pump may be used toevacuate the chamber 701 during a purge operation of ALE. Avalve-controlled conduit may be used to fluidically connect the vacuumpump to the processing chamber 701 so as to selectively controlapplication of the vacuum environment provided by the vacuum pump. Thismay be done employing a closed-loop-controlled flow restriction device,such as a throttle valve (not shown) or a pendulum valve (not shown),during operational plasma processing. Likewise, a vacuum pump and valvecontrolled fluidic connection to the capacitively coupled plasmaprocessing chamber may also be employed.

During operation of the apparatus, one or more process gases may besupplied through the gas flow inlets 760 and/or 770. In certainembodiments, process gas may be supplied only through the main gas flowinlet 760, or only through the side gas flow inlet 770. In some cases,the gas flow inlets shown in the figure may be replaced more complex gasflow inlets, one or more showerheads, for example. The Faraday shield749 and/or optional grid 750 may include internal channels and holesthat allow delivery of process gases to the chamber 701. Either or bothof Faraday shield 749 and optional grid 750 may serve as a showerheadfor delivery of process gases. In some embodiments, a liquidvaporization and delivery system may be situated upstream of the chamber701, such that once a liquid reactant or precursor is vaporized, thevaporized reactant or precursor is introduced into the chamber 701 via agas flow inlet 760 and/or 770. Example liquid precursors include SiCl₄and silicon amides.

Radio frequency power is supplied from the RF power supply 741 to thecoil 733 to cause an RF current to flow through the coil 733. The RFcurrent flowing through the coil 733 generates an electromagnetic fieldabout the coil 733. The electromagnetic field generates an inductivecurrent within the upper sub-chamber 702. The physical and chemicalinteractions of various generated ions and radicals with the wafer 719selectively etch features of and deposit layers on the wafer.

If the plasma grid is used such that there is both an upper sub-chamber702 and a lower sub-chamber 703, the inductive current acts on the gaspresent in the upper sub-chamber 702 to generate an electron-ion plasmain the upper sub-chamber 702. The optional internal plasma grid 750limits the amount of hot electrons in the lower sub-chamber 703. In someembodiments, the apparatus is designed and operated such that the plasmapresent in the lower sub-chamber 703 is an ion-ion plasma.

Both the upper electron-ion plasma and the lower ion-ion plasma maycontain positive and negative ions, though the ion-ion plasma will havea greater ratio of negative ions to positive ions. Volatile etchingand/or deposition byproducts may be removed from the lower sub-chamber703 through port 722. The chuck 717 disclosed herein may operate attemperatures ranging between about −200° C. and about 600° C. or betweenabout −20° C. and about 250° C. for processing a substrate to etchtantalum, the chuck 717 may be set at a temperature less than about 0°C. The temperature will depend on the process operation and specificrecipe and the tool used.

Chamber 701 may be coupled to facilities (not shown) when installed in aclean room or a fabrication facility. Facilities include plumbing thatprovide processing gases, vacuum, temperature control, and environmentalparticle control. These facilities are coupled to chamber 701, wheninstalled in the target fabrication facility. Additionally, chamber 701may be coupled to a transfer chamber that allows robotics to transfersemiconductor wafers into and out of chamber 701 using typicalautomation.

In some embodiments, a system controller 730 (which may include one ormore physical or logical controllers) controls some or all of theoperations of a processing chamber. The system controller 730 mayinclude one or more memory devices and one or more processors. In someembodiments, the apparatus includes a switching system for controllingflow rates and durations when disclosed embodiments are performed. Insome embodiments, the apparatus may have a switching time of up to about500 ms, or up to about 750 ms. Switching time may depend on the flowchemistry, recipe chosen, reactor architecture, and other factors.

In some implementations, a controller 730 is part of a system, which maybe part of the above-described examples. Such systems can comprisesemiconductor processing equipment, including a processing tool ortools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The controller 730, depending on the processingparameters and/or the type of system, may be programmed to control anyof the processes disclosed herein, including the delivery of processinggases, temperature settings (e.g., heating and/or cooling), pressuresettings, vacuum settings, power settings, radio frequency (RF)generator settings, RF matching circuit settings, frequency settings,flow rate settings, fluid delivery settings, positional and operationsettings, wafer transfers into and out of a tool and other transfertools and/or load locks connected to or interfaced with a specificsystem.

Broadly speaking, the controller 730 may be defined as electronicshaving various integrated circuits, logic, memory, and/or software thatreceive instructions, issue instructions, control operation, enablecleaning operations, enable endpoint measurements, and the like. Theintegrated circuits may include chips in the form of firmware that storeprogram instructions, digital signal processors (DSPs), chips defined asapplication specific integrated circuits (ASICs), and/or one or moremicroprocessors, or microcontrollers that execute program instructions(e.g., software). Program instructions may be instructions communicatedto the controller in the form of various individual settings (or programfiles), defining operational parameters for carrying out a particularprocess on or for a semiconductor wafer or to a system. The operationalparameters may, in some embodiments, be part of a recipe defined byprocess engineers to accomplish one or more processing steps during thefabrication of one or more layers, materials, metals, oxides, silicon,silicon dioxide, surfaces, circuits, and/or dies of a wafer. In someembodiments, controller 730 may be used to determine a window fortemperature for the modification operation of ALE, or to determine awindow for process conditions for the removal operation of ALE, or both.

The controller 730, in some implementations, may be a part of or coupledto a computer that is integrated with, coupled to the system, otherwisenetworked to the system, or a combination thereof. For example, thecontroller may be in the “cloud” or all or a part of a fab host computersystem, which can allow for remote access of the wafer processing. Thecomputer may enable remote access to the system to monitor currentprogress of fabrication operations, examine a history of pastfabrication operations, examine trends or performance metrics from aplurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the controller 730 receivesinstructions in the form of data, which specify parameters for each ofthe processing steps to be performed during one or more operations. Itshould be understood that the parameters may be specific to the type ofprocess to be performed and the type of tool that the controller isconfigured to interface with or control. Thus as described above, thecontroller 730 may be distributed, such as by comprising one or morediscrete controllers that are networked together and working towards acommon purpose, such as the processes and controls described herein. Anexample of a distributed controller for such purposes would be one ormore integrated circuits on a chamber in communication with one or moreintegrated circuits located remotely (such as at the platform level oras part of a remote computer) that combine to control a process on thechamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, an ALDchamber or module, an ALE chamber or module, an ion implantation chamberor module, a track chamber or module, and any other semiconductorprocessing systems that may be associated or used in the fabricationand/or manufacturing of semiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller might communicate with one or more of othertool circuits or modules, other tool components, cluster tools, othertool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

FIG. 8 depicts a semiconductor process cluster architecture with variousmodules that interface with a vacuum transfer module 838 (VTM). Thearrangement of transfer modules to “transfer” wafers among multiplestorage facilities and processing modules may be referred to as a“cluster tool architecture” system. Airlock 830, also known as aloadlock or transfer module, is shown in VTM 838 with four processingmodules 820 a-820 d, which may be individual optimized to performvarious fabrication processes. By way of example, processing modules 820a-820 d may be implemented to perform substrate etching, deposition, ionimplantation, wafer cleaning, sputtering, and/or other semiconductorprocesses. One or more of the substrate etching processing modules (anyof 820 a-820 d) may be implemented as disclosed herein, i.e., forintroducing a modification gas, for introducing a removal gas, and othersuitable functions in accordance with the disclosed embodiments. Airlock830 and process module 820 may be referred to as “stations.” Eachstation has a facet 836 that interfaces the station to VTM 838. Insideeach facet, sensors 1-18 are used to detect the passing of wafer 826when moved between respective stations.

Robot 822 transfers wafer 826 between stations. In one embodiment, robot822 has one arm, and in another embodiment, robot 822 has two arms,where each arm has an end effector 824 to pick wafers such as wafer 826for transport. Front-end robot 832, in atmospheric transfer module (ATM)840, is used to transfer wafers 826 from cassette or Front OpeningUnified Pod (FOUP) 834 in Load Port Module (LPM) 842 to airlock 830.Module center 828 inside process module 820 is one location for placingwafer 826. Aligner 844 in ATM 840 is used to align wafers.

In an exemplary processing method, a wafer is placed in one of the FOUPs834 in the LPM 842. Front-end robot 832 transfers the wafer from theFOUP 834 to an aligner 844, which allows the wafer 826 to be properlycentered before it is etched or processed. After being aligned, thewafer 826 is moved by the front-end robot 832 into an airlock 830.Because airlock modules have the ability to match the environmentbetween an ATM and a VTM, the wafer 826 is able to move between the twopressure environments without being damaged. From the airlock module830, the wafer 826 is moved by robot 822 through VTM 838 and into one ofthe process modules 820 a-320 d. In order to achieve this wafermovement, the robot 822 uses end effectors 824 on each of its arms. Oncethe wafer 826 has been processed, it is moved by robot 822 from theprocess modules 820 a-820 d to an airlock module 830. From here, thewafer 826 may be moved by the front-end robot 832 to one of the FOUPs834 or to the aligner 844.

It should be noted that the computer controlling the wafer movement canbe local to the cluster architecture, or can be located external to thecluster architecture in the manufacturing floor, or in a remote locationand connected to the cluster architecture via a network. A controller asdescribed above with respect to FIG. 7 may be implemented with the toolin FIG. 8.

EXPERIMENTAL

FIGS. 9A-9C shows an example of designer ALE. FIG. 9A shows operation A(modification) as a function of temperature, confirming that thereaction at 0° C. can be suppressed. At this setpoint substratetemperature, FIG. 9C shows bias scan based on two experiments, bothinvolving chlorine for modification and argon for removal in designerALE. The circle plots represent data collected for 40 cycles of ALE. Thesquare plots represent data collected for 25 cycles of ALE. The windowis confirmed to be ˜20-90 eV. This 70 eV window is the largest observedhere, as compared to the germanium ALE window being 10 eV in width andthe case study silicon ALE window is 20 eV in width. FIG. 9B furtherconfirms self-limiting behavior in time. Overall, synergy is greaterthan about 94% but may be limited by ellipsometry error. Overall, thismaterial showed high synergy ALE behavior. This was surprising giventhat tantalum reacted too quickly in an uncontrollable etching fashionat temperatures about 60° C. but after calculating the synergy andrelative energy values, performing ALE of tantalum at about or less thanabout 0° C. as the tool allows (such as between −200° C. and about 0°C.) resulted in self-limiting etching.

CONCLUSION

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe appended claims. It should be noted that there are many alternativeways of implementing the processes, systems, and apparatus of thepresent embodiments. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein.

What is claimed is:
 1. A method of etching a material on a substrate, the method comprising: identifying process conditions for an atomic layer etching process of the material using a modification gas and a removal gas; and performing the atomic layer etching process on the material on the substrate by: exposing the substrate to the modification gas to modify a surface of the material, the modification gas having a modification energy and a desorption energy with respect to the material to be etched, and exposing the modified surface to the removal gas and igniting a plasma to remove the modified surface, wherein the modification energy is less than the desorption energy, and the desorption energy is less than a surface binding energy of the material; wherein the identifying the process conditions comprises selecting a substrate temperature for performing the exposing the substrate to the modification gas, wherein the ion energy provided by the substrate temperature is between the modification energy and the desorption energy; and further comprising cooling the substrate to a temperature less than about 0° C. prior to performing the atomic layer etching process, and wherein the material is tantalum.
 2. The method of claim 1, wherein the identifying the process conditions further comprises selecting a bias power for applying a bias during the exposing the modified surface to the removal gas, wherein the ion energy provided by the bias is between the desorption energy and the surface binding energy.
 3. The method of claim 1, wherein the modification gas is selected to adsorb to the material without etching the material.
 4. The method of claim 1, wherein the removal gas is selected to remove the modified surface without etching underlying unmodified material.
 5. The method of claim 1, wherein the process conditions are selected from the group consisting of temperature, chamber pressure, plasma power, bias power, modification gas flow, and exposure time.
 6. The method of claim 1, further comprising modifying the process conditions within a process window.
 7. The method of claim 1, wherein the modification gas is a halogen-containing gas.
 8. The method of claim 1, wherein the removal gas is an inert gas.
 9. The method of claim 1, wherein atomic layer etching further comprises purging a chamber housing the substrate between the exposing the substrate to the modification gas and the exposing the substrate to the removal gas. 